Conventional optical fiber feedthrough designs utilize a metal tube brazed, i.e. soldered with a nonferrous alloy having a lower melting point than the metals being joined, to a housing wall with an optical fiber extending therethrough and soldered in the metal tube. Unfortunately, it is expensive to create a high quality bore through the metal tube with tight tolerances that closely match the optical fiber extending therethrough. Accordingly, most metal tubes have large inner diameters (ID), and require a solder, i.e. either metal or glass, to fill the gap around the optical fiber to create a hermetic seal. Unfortunately, metal and glass solders form a high compression force seal, which can cause damage or even breakage in the optical fibers.
At present, a single-mode fiber (SMF) coupled laser diode pump module 1, illustrated in FIG. 1, includes a housing 2, which utilizes a metal, e.g. Copper Tungsten (CuW), base 3 with a coefficient of thermal expansion (CTE) closely matched to a metal wall 4, e.g. Kovar, to enclose optical and electrical equipment 5. A metal tube 6 is then brazed to the housing wall 4 with an inner diameter much larger than the optical fiber 7 that will be inserted through the metal tube 6. To create a hermetic seal, the gap between the optical fiber 7 and the metal tube 6 is filled with high-melting-point solder 8, e.g. glass or metal, that flows around the optical fiber 7, which may be metalized. Metalization adds cost and the high-temperature-solder process may weaken the optical fiber 7 as well as add stress to the optical fiber 7 upon cooling, which can degrade optical-electrical performance of the module 1.
U.S. Pat. No. 4,707,065, entitled Optical Fibre Sealing Assembly, issued Nov. 17, 1987 to Peter Jenkins discloses a metallic ferrule held in a bulkhead using an externally threaded retaining member with a sealing ring therebetween.
U.S. Pat. Nos. 4,904,046, entitled Process of and Apparatus for Leading an Optical Waveguide Through a Wall Via a Hermetic Seal, issued Feb. 27, 1990 to Paschke et al; 5,177,806, entitled Optical Fiber Feedthrough issued Jan. 5, 1993 to Abbott et al; 5,509,952, entitled Method for Bonding a Fiber to a Sleeve for Fiber Optic Packaging Applications issued Apr. 23, 1996 to Moore et al; 5,613,031, entitled Hermetically Sealed Optical Fiber Insert Structure issued Mar. 18, 1997 to Tanabe et al; 5,658,364, entitled Method of Making Fiber Optic-To-Metal Connection Seal, issued Aug. 19, 1997 to DeVore et al; 5,970,194 entitled Optical Fiber Having Hermetically Sealable Section, issued Oct. 19, 1999 to Dunn et al; 6,837,075, entitled Glass Fiber Fixative and Fixing Process, issued Jan. 4, 2005 to Snowdon et al; 6,901,203, entitled Fiber Optic Feed-Through Tube and Method for Making the Same, issued May 31, 2005 to Czubarow et al; and 6,922,518, entitled Method and Apparatus for Sealed Fiber Optic Feedthroughs issued Jul. 26, 2005 to Gerard Esposito each disclose the use of a metallic ferrule welded or metallically soldered to the outer wall of a housing with a glass solder sealing the fiber into the metallic ferrule.
U.S. Pat. No. 5,815,619, entitled Fiber Optic Connector Hermetically Terminated, issued Sep. 29, 1998 to Cary Bloom discloses an optical fiber sealed within a ferrule using molten metal.
U.S. Pat. No. 6,220,766, entitled Hermetically Sealed Package and Method of Assembly, issued Apr. 24, 2001 to Yeandle et al discloses a metal ferrule welded to a metal housing.
U.S. Pat. No. 6,643,446, entitled Hermetic Fiber Ferrule and Feedthrough, issued Nov. 4, 2003 to Moidu, Abdul Jaleel K. and Moore, William Thomas discloses a pair of glass sleeves within a outer metal sleeve, which is abutted against and welded to the housing of a module. A glass solder seals the fiber to the glass sleeves and the glass sleeves to the outer metal sleeve, and the end of the outer metal sleeve is fixed to the face of the module housing.
An object of the present invention is to overcome the shortcomings of the prior art by eliminating the use of metal solder around the ferrule and glass solder around the optical fiber by providing a ceramic ferrule that can be glass soldered to the housing, and which has an inner diameter closely matching the fiber OD so that an epoxy can be used to fill the gap and create a hermetic seal. Epoxy has advantages over solder, which require high temperature and introduce stress upon cooling that may weaken the fiber or lead to a reduction in the polarization extinction ratio of the optical signal.